1. Field of the Invention
The present invention relates to a semiconductor device. In particular, the invention relates to a semiconductor device in which an antenna circuit, an electric double layer capacitor, and a signal processing circuit including a charging circuit are formed over a substrate.
2. Description of the Related Art
In recent years, RFID (radio frequency identification) tags have been attracting attention as a semiconductor device that communicates information by radio. The RFID tags (hereinafter, simply referred to as RFID) are also referred to as IC (integrated circuit) tags, IC chips, RF tags, wireless tags, or electronic tags. RFID has been utilized for production, management, and the like of individual objects, and has been expected to be applied to personal identification as well.
RFID can be classified into active-type RFID and passive-type RFID depending on whether a power source is incorporated in the RFID or a power source is supplied from the outside (as for the active-type RFID, see Reference 1: Japanese Published Patent Application No. 2005-316724 and, as for the passive-type RFID, see Reference 2: Japanese Translation of PCT International Application No. 2006-503376). The active-type RFID has a built-in battery as a power source for driving the RFID, whereas the passive-type RFID utilizes electricity, which is generated from radio waves or electromagnetic waves (carrier waves) from the outside, as a power source for driving the RFID so that a structure without a battery is realized.
FIG. 25 is a block diagram illustrating a specific structure of an active-type RFID. In an active-type RFID 3100 of FIG. 25, a communication signal received by an antenna circuit 3101 is input to a demodulation circuit 3105 and an amplifier 3106 in a signal processing circuit 3102. Communication signals are usually transmitted after processing of 13.56 MHz carriers or 915 MHz carriers through ASK modulation, PSK modulation, or the like. FIG. 25 illustrates an example in which 13.56 MHz carriers are used for the communication signals. In FIG. 25, a clock signal that is a reference for processing a signal is necessary, and a 13.56 MHz carrier is used as a clock here. The amplifier 3106 amplifies the 13.56 MHz carrier and supplies it to a logic circuit 3107 as the clock. In addition, the ASK modulated communication signal or the PSK modulated communication signal is demodulated by the demodulation circuit 3105. The demodulated signal is also transmitted to and analyzed by the logic circuit 3107. The signal analyzed by the logic circuit 3107 is transmitted to a memory control circuit 3108. In response to the signal, the memory control circuit 3108 controls a memory circuit 3109, and data stored in the memory circuit 3109 is retrieved and transmitted to a logic circuit 3110. The signal is encoded by the logic circuit 3110 and then amplified by an amplifier 3111 so that a modulation circuit 3112 modulates the signal. A power source is supplied from a battery 3103 provided outside the signal processing circuit 3102 through a power source circuit 3104. The power source circuit 3104 supplies electricity to the amplifier 3106, the demodulation circuit 3105, the logic circuit 3107, the memory control circuit 3108, the memory circuit 3109, the logic circuit 3110, the amplifier 3111, the modulation circuit 3112, and the like. In such a manner, the active-type RFID operates.
However, since the active-type RFID has the built-in battery 3103, the active-type RFID becomes inactive once the battery has run out. Therefore, it is necessary to control the lifetime of the battery or replace the battery after the battery has run out. However, a case is possible in which the battery cannot be replaced immediately after the operation of the RFID tag has stopped, depending on the circumstance in use.
In addition, when the built-in battery of the active-type RFID has run out of electric energy, the active-type RFID becomes unresponsive to signals from a reader. In that case, it is difficult for users to easily determine the reason why the RFID is unresponsive, that is, whether the battery has run out or there may be other reasons such as a bad reception state of radio waves or some problems with the reader.
FIG. 26 is a block diagram illustrating a specific structure of a passive-type RFID. In a passive-type RFID 3200 of FIG. 26, a communication signal received by an antenna circuit 3201 is input to a demodulation circuit 3205 and an amplifier 3206 in a signal processing circuit 3202. Communication signals are usually transmitted after processing of 13.56 MHz carriers or 915 MHz carriers through ASK modulation, PSK modulation, or the like. In FIG. 26, a clock signal that is a reference for processing a signal is necessary, and a 13.56 MHz carrier is used as the clock here. The amplifier 3206 amplifies the 13.56 MHz carrier and supplies it to a logic circuit 3207 as the clock. In addition, the ASK modulated communication signal or the PSK modulated communication signal is demodulated by the demodulation circuit 3205. The demodulated signal is also transmitted to and analyzed by the logic circuit 3207. The signal analyzed by the logic circuit 3207 is transmitted to a memory control circuit 3208. In response to the signal, the memory control circuit 3208 controls a memory circuit 3209, and data stored in the memory circuit 3209 is retrieved and transmitted to a logic circuit 3210. The signal is encoded by the logic circuit 3210 and then amplified by an amplifier 3211 so that a modulation circuit 3212 modulates the signal. On the other hand, the communication signal input to a rectifier circuit 3203 is rectified and input to a power source circuit 3204. The power source circuit 3204 supplies electricity to the amplifier 3206, the demodulation circuit 3205, the logic circuit 3207, the memory control circuit 3208, the memory circuit 3209, the logic circuit 3210, the amplifier 3211, the modulation circuit 3212, and the like. In such a manner, the passive-type RFID operates.
However, the passive-type RFID has a problem in that it is active only when located within the range that the RFID can receive radio waves or electromagnetic waves (carrier waves) from a reader/writer that is a transmission source of electricity. That is, the passive-type RFID is active only in the vicinity of a reader/writer.
In order to solve the aforementioned problems, there is known a method of providing a battery as a power source for supplying electricity to the RFID. Accordingly, the RFID can be used even when it is not receiving radio waves or electromagnetic waves (carrier waves) from the outside. In distribution systems and the like, in particular, an electric double layer capacitor that is compact and has high capacity is generally mounted as a battery on the RFID.
However, even when such a compact electric double layer capacitor is mounted on the RFID, the RFID itself becomes large or thick, although the RFID is desirably thin and lightweight.
In addition, when an anisotropic conductive film, in which conductive spacers are dispersed in a thermosetting resin or a photo-curing resin, is used for mounting the electric double layer capacitor on the RFID, reliability of the connection portion becomes low when the RFID is subjected to high-temperature conditions because the thermal expansion rates and the thermal contraction rates of the electric double layer capacitor and the RFID differ from one another.
In order to solve the foregoing problems, there is known a method of integrating an electric double layer capacitor into an RFID, for example by forming an electric double layer capacitor to be adjacent to a signal processing circuit that is constructed from CMOS (see Reference 3: Japanese Published Patent Application No. 2006-024087).